Different rates apply depending on how long you stay.
Chapter and verse is here:
http://www.revenue.ie/en/tax/it/leaflets/it54.html
..and some cut and pasted from the relevant bits
Schedule based on current Civil Service Subsistence Rates for absences outside the State
Details of quantum of Civil Service subsistence rates for certain foreign countries are available from any Regional Revenue Office.
The Civil Service schedule of rates may be applied in the following manner in respect of temporary (up to six months) absence:
Civil Service rates
Period of Assignment Abroad % of Subsistence Rate for relevant location
First month 100%
Second and Third month 75%
Fourth, Fifth and Sixth month 50%
The rates may be used only in respect of the reimbursement of allowable subsistence expenses where the employee is working abroad on a foreign assignment. "Working abroad" on foreign assignment” means that the employee is actually performing the duties of the employment abroad for a temporary period. Where actual vouched expenses exceed the flat rate allowances such vouched expenses may be used instead of flat rate allowances.
Long term Absences
For long term absences (where assignment period is greater than six months), reimbursement of allowable subsistence expenses may be made in the following manner:
allowable subsistence expenses
Period of Assignment Abroad Allowable Subsistence
First month of assignment (to facilitate the employee obtaining self catering accommodation) Up to the Overnight Rate
Remainder of Assignment Up to the cost of reasonable accommodation plus 50% of the day rate (10 hours) for the location